javascript Design patttern need feedback

class Song {
    constructor(title, artist, format) {
      this.title = title;
      this.artist = artist;
      this.format = format;
    }
  }
  
  // Decoder.js (Strategy Pattern)
  class Decoder {
    decode(format) {
      return `Decoding ${format} format...`;
    }
  }
  
  class Mp3Decoder extends Decoder {
    decode(format) {
      return `Decoding MP3 format: ${format}...`;
    }
  }
  
  class WavDecoder extends Decoder {
    decode(format) {
      return `Decoding WAV format: ${format}...`;
    }
  }
  
  // MusicPlayer.js (Observer Pattern - Subject)
class MusicPlayer {
    constructor() {
      this.observers = [];
    }
  
    play(song) {
      const message = `Playing song: ${song.title} - ${song.artist}`;
      this.notifyObservers();
      return message;
    }
  
    registerObserver(observer) {
      this.observers.push(observer);
    }
  
    removeObserver(observer) {
      const index = this.observers.indexOf(observer);
      if (index !== -1) {
        this.observers.splice(index, 1);
      }
    }
  
    notifyObservers() {
      this.observers.forEach((observer) => console.log(observer.update()));
    }
  }
  
  
  // Observer.js (Observer Pattern)
  class Observer {
    constructor() {
      this.subject = null;
    }
  
    setSubject(subject) {
      this.subject = subject;
      this.subject.registerObserver(this);
    }
  
    update() {
      // UI update logic when music playback changes
      return "Updating UI...";
    }
  }
  
  // DecoderFactory.js (Factory Pattern)
  class DecoderFactory {
    createDecoder(format) {
      switch (format) {
        case "MP3":
          return new Mp3Decoder();
        case "WAV":
          return new WavDecoder();
        default:
          throw new Error(`Decoder not available for format: ${format}`);
      }
    }
  }
  
  // Playlist.js (Composite Pattern)
  class Playlist {
    constructor(name) {
      this.name = name;
      this.songs = [];
    }
  
    addSong(song) {
      this.songs.push(song);
    }
  
    removeSong(song) {
      const index = this.songs.findIndex(
        (s) => s.title === song.title && s.artist === song.artist
      );
      if (index !== -1) {
        this.songs.splice(index, 1);
      }
    }
  }
  
  // MusicFacade.js (Facade Pattern)
class MusicFacade {
    constructor() {
      this.streamingService = {
        subscribed: false,
      };
      //this.paymentService = {}; // 수정된 부분
      this.musicPlayer = new MusicPlayer();
      this.decoderFactory = new DecoderFactory();
      this.playlists = [];
    }
  
    subscribe() {
      //  //=this.paymentService.processPayment();
      this.streamingService.subscribed = true;
      return "Subscribed to the music streaming service.";
    }
  
    unsubscribe() {
      this.streamingService.subscribed = false;
      return "Unsubscribed from the music streaming service.";
    }
  
    playMusic(song) {
      if (this.streamingService.subscribed) {
        const decoder = this.decoderFactory.createDecoder(song.format);
        const decodeMessage = decoder.decode(song.format);
        const playMessage = this.musicPlayer.play(song);
        return `${decodeMessage}\n${playMessage}`;
      } else {
        return "You need to subscribe to the music streaming service to play music.";
      }
    }
  
    createPlaylist(name) {
      const playlist = new Playlist(name);
      this.playlists.push(playlist);
      return `Created playlist: ${name}`;
    }
  
    addSongToPlaylist(song, playlistName) {
      const playlist = this.playlists.find((p) => p.name === playlistName);
      if (playlist) {
        playlist.addSong(song);
        return `Added song to playlist: ${playlistName}`;
      } else {
        return `Playlist not found: ${playlistName}`;
      }
    }
  
    removeSongFromPlaylist(song, playlistName) {
      const playlist = this.playlists.find((p) => p.name === playlistName);
      if (playlist) {
        playlist.removeSong(song);
        return `Removed song from playlist: ${playlistName}`;
      } else {
        return `Playlist not found: ${playlistName}`;
      }
    }
  }
  
  // Usage
  const musicFacade = new MusicFacade();
  console.log(musicFacade.subscribe());
  
  const observer = new Observer();
  const song = new Song("Song Title", "Artist", "MP3");
  observer.setSubject(musicFacade.musicPlayer);
  musicFacade.musicPlayer.registerObserver(observer);
  
  console.log(musicFacade.playMusic(song));
  console.log(musicFacade.createPlaylist("My Playlist"));
  console.log(musicFacade.addSongToPlaylist(song, "My Playlist"));
  console.log(musicFacade.removeSongFromPlaylist(song, "My Playlist"));
  console.log(musicFacade.unsubscribe());
  

Music Streaming Service Development

• The Facade pattern is used to determine whether the user is a member or not.

• The Strategy pattern is used to handle various music formats, such as MP3 and WAV.

• The Observer pattern is used to monitor the music playback status, where the Subject interface is defined to update the UI whenever there are any changes.

• The Factory pattern is used to create objects necessary for music playback. For example, when playing music in MP3 format, an MP3Decoder object is created, and when playing music in WAV format, a WavDecoder object is created.

• The Composite pattern is used to construct music playlists.

  Can you please review the design pattern I have created and provide feedback on any strange or incorrect parts? I would greatly appreciate your feedback.

I would comment that this looks like you have just learned design patterns and you are looking to implement them in code. And it is precisely the same thing that has happened to all of us that read the Gang of Four book: you are going a little overboard.

While this sounds critical (and is, to an extent), it's an entirely normal progression, and I did much worse. To answer your specific question, I would say that your implementations look correct from what I remember of those patterns.

However, if I were in a code review with you, I would suggest toning down the pattern-ness of it all. For example, don't look to use the Strategy pattern; just use it. I also would not name things after patterns at this stage of my career. Just returning an interface that has a 'play' method pretty much conveys what you are doing - you don't have to say 'Strategy pattern here!'

Finally, I would look to be a bit more idiomatic. For example, rather than using the subscriber pattern, I would use emit native JavaScript events from the player and let the UI decide what to do with it - no need to subscribe to anything.

To be honest, this looks more like what Java looked like when I was coding Java. I suspect this type of coding might still be more idiomatic in that community (although that was many years ago).

So finally, it looks great. Keep it up. And over time, you will find that as you internalise the patterns, you will stop explicitly using them, but more coding structures that fit your specific need.